1. Field of the Invention
The invention relates to a cooling technique in drive units for electric cars and drive units for hybrid cars.
2. Description of Related Art
When an electric motor is used as a power source for vehicles, the electric motor needs a control device (an inverter in the case of an AC electric motor) that controls the electric motor. Since the control device, for example, the inverter, is connected to the electric motor by way of a power cable, the control device can be arranged in an appropriate position apart from the electric motor. For the convenience of a car-mounted arrangement, it is desired that the control device be united with the electric motor.
By the way, current control devices are lower in heat-resistant temperature than electric motors. Hereupon, when a control device is to unite with an electric motor in the above-mentioned manner, certain devices that cut off direct heat conduction from the electric motor to the control device is needed in order to protect the control device. Also, since the temperature of the control device is raised due to heat generation by the elements of the control device, cooling is necessary in order to maintain the control device at the heat-resistant temperature thereof or lower.
Conventionally, U.S. Pat. No. 5,491,370 describes a technique that is thought to be useful for improving such a problematic matter. This technique adopts a construction in which a cooling channel (spiral passage) is formed on an outer periphery of a cylindrical-shaped inner body (housing) of an electric motor. A cooling saddle is also formed on a part of a jacket (sleeve) externally mounted on the housing in a manner that covers an opening surface side of the passage with a control housing receiving therein an IGBT module (inverter component) mounted on the cooling saddle. With this construction, a cooling space is defined on facing portions of the control housing and the cooling saddle. Circulation of the cooling fluid is carried out with the cooling fluid, fed from a water pump, flowing to the spiral passage via the cooling space, passing through a heat exchanger and returning to the water pump.
Also, another technique is proposed in JP-A-5-292703 and adopts a construction in which a motor body and a controller are united together with a heat sink therebetween. A cooling liquid is allowed to flow through an interior of the heat sink to cool the controller and the cooling liquid having flowed is fed to the motor body to cool the motor body.